Three duplex modes are currently supported by a Long Term Evolution (LTE) system: the Frequency Division Duplex (FDD) mode as illustrated in FIG. 1A, the Half-Frequency Division Duplex (H-FDD) mode as illustrated in FIG. 1B, and the Time Division Duplex (TDD) mode as illustrated in FIG. 1C.
Here the FDD refers to uplink transmission and downlink transmission in different carrier frequency bands to allow simultaneous reception and transmission by an evolved Node B (eNB) and a User Equipment (UE). To support simultaneous reception and transmission, the FDD devices need to be provided with two sets of transceivers and duplex filters. The H-FDD differs from the FDD in that the UE does support simultaneous reception and transmission, that is, the eNB in the H-FDD is the same as the eNB in the FDD, but the UE in the H-FDD can be simplified relative to the UE in the FDD by maintaining only one of the sets of transceivers and saving a cost of the duplex filters. The TDD refers to uplink transmission and downlink transmission in the same carrier frequency band to allow transmission (reception) or reception (transmission) of a channel by the eNB (UE) respectively in different periods of time.
There is only one carrier in a cell in the LTE and earlier wireless communication systems, and there is a bandwidth up to 20 MHz in the LTE system, as illustrated in FIG. 2.
In a Long Term Evolution-Advanced (LTE-A) system, there are required peak rates of the system, up to 1 Gbps in the downlink and 500 Mbps in the uplink, as improved significantly over the LTE system. The required peak rates can not be available with only one carrier with a bandwidth up to 20 MHz. It is thus necessary in the LTE-A system to extend a bandwidth available to the UE, and in view of this, the technology of Carrier Aggregation (CA) has been introduced where a plurality of contiguous or non-contiguous carriers served by the same eNB (eNB) are aggregated together to serve the UE concurrently with a desirable rate. These carriers aggregated together are also referred to as Component Carriers (CCs). Each cell can be a component carrier, and cells (component carriers) served by different eNBs can not be aggregated. In order to ensure the UE in the LTE to be able to operate over each of the aggregated carriers, there is a bandwidth of no more than 20 MHz for each of the carriers. FIG. 3 illustrates the CA technology in the LTE-A.
There are four carriers, served by the eNB in the LTE-A system illustrated in FIG. 3, which can be aggregated, and over which the eNB can transmit data concurrently with the UE to thereby improve the throughput of the system.
At present, no carrier aggregation across the systems can be supported in the LTE, that is, an FDD carrier can only be aggregated with an FDD carrier, and a TDD carrier can only be aggregated with a TDD carrier.
In the LTE system, a radio frame is of 10 ms and a subframe is of 1 ms in both the FDD mode and the TDD mode. Seven TDD uplink/downlink configurations are defined for one TDD radio frame, as depicted in Table 1 below, where D represents a downlink (DL) subframe, U represents an uplink (UL) subframe, and S represents a special subframe of the TDD system.
TABLE 1Uplink/downlinkconfig-Subframe numberuration01234567890DSUUUDSUUU1DSUUDDSUUD7DSUDDDSUDD3DSUUUDDDDD4DSUUDDDDDD5DSUDDDDDDD6DSUUUDSUUD
In the LTE FDD system, the UE receives downlink data in a subframe (n−4), then feeds back signaling of whether data received in the downlink subframe (n−4) needs to be retransmitted, that is, feeds back Acknowledgement/Negative Acknowledgement (ACK/NACK) information, in an uplink subframe n. When carriers are aggregated, ACK/NACK information corresponding to a plurality of downlink carriers in the subframe n−4 will be fed back concurrently in the uplink subframe n.
In the LTE TDD system, the UE may feed back, ACK/NACK information corresponding to multiple downlink subframes, in one uplink subframe, that is, the UE detects transmission of a Physical Downlink Shared Channel (PDSCH), or a Physical Downlink Control Channel (PDCCH) indicating downlink semi-persistent scheduling release, in a downlink subframe (n−k) and feeds back corresponding ACK/NACK information in an uplink subframe n, where kεK, and values in the set K depend upon the TDD uplink/downlink configuration of the system, and the particular subframe number, as depicted in Table 2. Especially, there is no ACK/NACK feedback for the special subframe when the special subframe configuration 0 and 5 are used for normal Cyclic Prefix (CP) and the special subframe configuration 0 and 4 are used for extended CP, that is, the UE will not feed back ACK/NACK for special subframe.
TABLE 2Uplink/downlinkConfig-Subframe numberuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7,————8, 7,——4, 64, 63——7, 6, 116, 55, 4—————4——12, 8,6, 5,——————7, 114, 75——13, 12, 9,———————8, 7, 5,4, 11, 66——775——77—
In Table 2, a plurality of radio frames are arranged in order, that is, if the last subframe in the radio frame a is k, then the first subframe in the radio frame a+1 is k+1, and Table 2 depicts K corresponding to respective uplink subframes taking only one radio frame as an example, where n−k<0 indicates a downlink subframe in a preceding radio frame.
In summary, there has been absent so far a solution to feeding back ACK/NACK information for downlink data, applicable to carrier aggregation with carriers in the TDD system and carriers the FDD system.